1. Field of the Invention
The present invention relates to a seat belt system, which protects an occupant of a vehicle by restraining the occupant, more specifically, to a pre-crash seat belt, which retracts a seat belt prior to an unavoidable vehicle collision after the unavoidable vehicle collision is predicted.
2. Description of Related Art
One known vehicle occupant protective system is called a pre-crash seat belt system, which retracts a seat belt prior to an unavoidable vehicle collision after the unavoidable vehicle collision is predicted based on corresponding information, such as a following distance relative to a front vehicle or a brake operation by a vehicle driver (see, for example, Japanese Unexamined Patent Publication No. H06-286581 corresponding to U.S. Pat. No. 5,552,986).
The above seat belt system restrains the occupant by the seat belt with a fixed tension regardless of a body size and a weight of the occupant on a vehicle seat when it is determined that the vehicle collision is unavoidable. However, at the time of fastening the seat belt, a contact position of the seat belt relative to the body of the occupant and a restraining force of the seat belt vary from occupant to occupant depending on the body size of the occupant. Thus, even when the seat belt is retracted prior to the collision, the restraining force of the seat belt may be too weak for some occupants or may be too strong for some other occupants. In each of these cases, the occupant has uncomfortable feeling, and the sufficient occupant protection cannot be achieved.